The objective of the research is to investigate the use of cultured lymphocytes from allogeneic, H-2-compatible donor mice for successful adoptive immunotherapy of murine (AKR) leukemia. Using limiting dilution techniques, lymphocytes from alloimmunized donor mice are maintained in culture with T-cell growth factor (TCGF). Functionally restricted cytolytic and helper T cells with specificity for leukemic or nonleukemic cells are selected for study. Expanded cultured cells are studied in vivo for antitumor and antihost reactivity, tissue distribution, functional life-span and sensitivity to exogenous TCGF. Additional studies focus on the nature of the antigenic targets on leukemia cells. Alloimmunization-induced antileukemia-reactive cells have heterogeneous cytotoxic specificities; some are H-2 restricted and appear to be specific for non-H-2-encoded antigens, while others mediate unrestricted killing. Bulk cultured and cloned cytolytic cells can kill leukemia cells in vivo, but lung migration poses a major barrier to successful immunotherapy.